net/smc: fix warning in smc_rx_splice() when calling get_page()

smc_lo_register_dmb() allocates DMB buffers with kzalloc(), which are
later passed to get_page() in smc_rx_splice(). Since kmalloc memory is
not page-backed, this triggers WARN_ON_ONCE() in get_page() and prevents
holding a refcount on the buffer. This can lead to use-after-free if
the memory is released before splice_to_pipe() completes.

Use folio_alloc() instead, ensuring DMBs are page-backed and safe for
get_page().

WARNING: CPU: 18 PID: 12152 at ./include/linux/mm.h:1330 smc_rx_splice+0xaf8/0xe20 [smc]
CPU: 18 UID: 0 PID: 12152 Comm: smcapp Kdump: loaded Not tainted 6.17.0-rc3-11705-g9cf4672ecfee #10 NONE
Hardware name: IBM 3931 A01 704 (z/VM 7.4.0)
Krnl PSW : 0704e00180000000 000793161032696c (smc_rx_splice+0xafc/0xe20 [smc])
           R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3
Krnl GPRS: 0000000000000000 001cee80007d3001 00077400000000f8 0000000000000005
           0000000000000001 001cee80007d3006 0007740000001000 001c000000000000
           000000009b0c99e0 0000000000001000 001c0000000000f8 001c000000000000
           000003ffcc6f7c88 0007740003e98000 0007931600000005 000792969b2ff7b8
Krnl Code: 0007931610326960: af000000		mc	0,0
           0007931610326964: a7f4ff43		brc	15,00079316103267ea
          #0007931610326968: af000000		mc	0,0
          >000793161032696c: a7f4ff3f		brc	15,00079316103267ea
           0007931610326970: e320f1000004	lg	%r2,256(%r15)
           0007931610326976: c0e53fd1b5f5	brasl	%r14,000793168fd5d560
           000793161032697c: a7f4fbb5		brc	15,00079316103260e6
           0007931610326980: b904002b		lgr	%r2,%r11
Call Trace:
 smc_rx_splice+0xafc/0xe20 [smc]
 smc_rx_splice+0x756/0xe20 [smc])
 smc_rx_recvmsg+0xa74/0xe00 [smc]
 smc_splice_read+0x1ce/0x3b0 [smc]
 sock_splice_read+0xa2/0xf0
 do_splice_read+0x198/0x240
 splice_file_to_pipe+0x7e/0x110
 do_splice+0x59e/0xde0
 __do_splice+0x11a/0x2d0
 __s390x_sys_splice+0x140/0x1f0
 __do_syscall+0x122/0x280
 system_call+0x6e/0x90
Last Breaking-Event-Address:
smc_rx_splice+0x960/0xe20 [smc]
---[ end trace 0000000000000000 ]---

Fixes: f7a22071dbf3 ("net/smc: implement DMB-related operations of loopback-ism")
Reviewed-by: Mahanta Jambigi <mjambigi@linux.ibm.com>
Signed-off-by: Sidraya Jayagond <sidraya@linux.ibm.com>
Link: https://patch.msgid.link/20250917184220.801066-1-sidraya@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions